1. Field of the Invention
The present invention relates to an optical disc device which is used when reproduction of information recorded in an optical disc is performed, or recording of information in an optical disc is performed.
2. Description of Related Art
From the past, in an optical pickup provided in an optical disc device, there are some optical pickup including a spherical aberration correction mechanism in order to perform correction of the spherical aberration (for example, see patent documents 1 to 4).
FIG. 9 is a schematic diagram to show an example of structure of a conventional optical pickup including a spherical aberration correction mechanism. In the conventional optical pickup 10, laser light emitted from a light source 101 is divided by a diffraction element 102 into main light and two sub lights, and reflected by a polarization beam splitter 103. The laser light reflected by the polarization beam splitter 103 is converted by a quarter wave plate 104 into circular polarized light, and passes through a collimator lens 105. The laser light which passes though the collimator lens 105 is reflected by a raising mirror 106, and is focused by an object lens 107 on an information recording layer 100a of an optical disc 100. Returned light reflected by the information recording layer 100a of the optical disc 100 passes through the object lens 107, the raising mirror 106, and the collimator lens 105 in this order, and is converted by the quarter wave plate 104 into linear polarized light. The returned light converted into the linear polarized light passes through the polarization beam splitter 103, is given astigmatism by a cylindrical lens 108, and is gathered into a photo detector 109.
The photo detector 109 converts received light signal into electric signal. The converted electric signal is processed by a signal processing device which is not shown, to generate reproduced RF signal, focus error signal (FE signal), tracking error signal (TE signal) and the like. An object lens actuator 20 is driven based on the generated FE signal and TE signal, to perform focus servo control and tracking servo control. In this respect the focus servo control is a control to be performed so that positional relation between the object lens 107 and the optical disc 100 is kept in a constant relation. Further, the tracking servo control is a control to be performed so that a beam spot focused by the object lens 107 always traces a track formed on the optical disc 100.
By the way, in a conventional optical pickup 10, the collimator lens 105 can be moved along a light axis direction (direction shown by arrow A in FIG. 9) by a lens moving portion 30. By adjusting position of the collimator lens 105 along the light axis direction, a converging state or a diverging state of light output from the collimator lens 105 can be adjusted. By this arrangement, correction of spherical aberration can be performed through adjustment of the converging state and the diverging state of light input to the object lens 107 by adjusting position of the collimator lens 105 by the lens moving portion 30 along the light axis direction. That is, the conventional optical pickup 10 includes a spherical aberration correction mechanism composed by the collimator lens 105 and the lens moving portion 30.
FIG. 10 is a schematic perspective view to show an example of structure of the lens moving portion provided in the conventional optical pickup. The lens moving portion 30 included in the conventional optical pickup 10 is provided with a stepping motor 301, a lead screw 302, a lead nut 303, a lens holder 304, two guide shafts 305a, 305b, a pressure spring 306, and a photo interrupter 307, as shown in FIG. 10. For example, the lens moving portion 30 may be fixed directly on a base, not shown, which is provided in the optical pickup 10.
When the stepping motor 301 is driven, the lead screw 302 that is fixed on an output axis of the stepping motor 301, is rotated. The lead nut 303 is moved in a direction which is parallel to a longer direction of the lead screw 302 along with rotation of the lead screw 302. In this respect, moving direction of the lead nut 303 is changed by rotating direction of the stepping motor 301.
The lens holder 304 having a through hole 304a to hold the collimator lens 105, is configured to slide along two guide shafts 305a, 305b which extend in a direction that is parallel to the light axis of the collimator lens 105. The pressure spring 306 which is formed in a coil shape, is fitted freely on one of the guide shaft 305a to give biasing force to the lens holder 304.
When the lead nut 303 is moved away from the stepping motor 301, the lens holder 304 is pushed by the lead nut 303 and is moved against the biasing force of the pressure spring 306. On the other hand, when the lead nut 303 is moved toward the stepping motor 301, the lens holder 304 is pushed by the biasing force of the pressure spring 306 and is moved while contacted with the lead nut 303.
In the lens holder 304, a protruding portion 304b is provided so that detection by the photo interrupter 307 becomes possible. When this protruding portion 304b interrupts light from a light emitting part to a light receiving part (both are not shown) of the photo interrupter 307, it is judged that the lens holder 304 exists at a reference position by the photo interrupter 307. Then, position of the lens holder 307 is controlled by using amount of steps of the stepping motor 301 from the reference position.
The optical pickup 10 including this kind of the spherical aberration correction mechanism is convenient because correction of the spherical aberration can be performed by only performing the positional adjustment of the collimator lens 105 in the light axis direction utilizing the abovementioned lens moving portion 30.    [Patent Document 1] JP-A-2001-250256    [Patent Document 2] JP-A-2007-328827    [Patent Document 3] JP-A-2004-342221    [Patent Document 4] JP-A-2007-026611